Physics – Plasma Physics
Scientific paper
Aug 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010jgra..11500f17s&link_type=abstract
Journal of Geophysical Research, Volume 115, Issue 9, CiteID A00F17
Physics
Plasma Physics
7
Magnetospheric Physics: Plasma Waves And Instabilities (2471), Space Plasma Physics: Wave/Particle Interactions (2483, 6984), Magnetospheric Physics: Numerical Modeling, Magnetospheric Physics: Radiation Belts, Space Plasma Physics: Mathematical And Numerical Techniques (0500, 3200)
Scientific paper
On July 24, 2003, when the Cluster 4 satellite crossed the magnetic equator at about 4.5 RE radial distance on the dusk side (˜15 MLT), whistler wave emissions were observed below the local electron gyrofrequency (fce) in two bands, one band above one-half the gyrofrequency (0.5fce) and the other band below 0.5fce. A careful analysis of the wave emissions for this event has shown that Cluster 4 passed through the wave source region. Simultaneous electron particle data from the PEACE instrument in the generation region indicated the presence of a mid-energy electron population (˜100 s of eV) that had a highly anisotropic temperature distribution with the perpendicular temperature 10 times the parallel temperature. To understand this somewhat rare event in which the satellite passed directly through the wave generation region and in which a free energy source (i.e., temperature anisotropy) was readily identified, a linear theory and particle in cell simulation study has been carried out to elucidate the physics of the wave generation, wave-particle interactions, and energy redistribution. The theoretical results show that for this event the anisotropic electron distribution can linearly excite obliquely propagating whistler mode waves in the upper frequency band, i.e., above 0.5fce. Simulation results show that in addition to the upper band emissions, nonlinear wave-wave coupling excites waves in the lower frequency band, i.e., below 0.5fce. The instability saturates primarily by a decrease in the temperature anisotropy of the mid-energy electrons, but also by heating of the cold electron population. The resulting wave-particle interactions lead to the formation of a high-energy plateau on the parallel component of the warm electron velocity distribution. The theoretical results for the saturation time scale indicate that the observed anisotropic electron distribution must be refreshed in less than 0.1 s allowing the anisotropy to be detected by the electron particle instrument, which takes several seconds to produce a distribution.
Ashour-Abdalla Maha
Coroniti Ferdinan V.
Decyk Viktor
Fazakerley Andrew N.
Goldstein Michel L.
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